Understanding brain pathways and neurotransmitter systems that regulate ingestion is essential to development of pharmacological tools to help patients regulate food intake. Taste is a major factor driving over&#8208;eating so it is important to understand the neurotransmitter systems involved in early transmission of taste information to the brain. The experiments in this proposal will test the proposition that good&#8208;tasting (appetitive) foods, i.e. those rich in sugars and glutamate, activate neurochemically distinct circuits in the brainstem taste relay nuclei than do unpleasant&#8208;tasting (aversive) tastes. The experiments rely on induced expression of the immediate&#8208;early gene, c&#8208;fos, as a marker of taste&#8208;activated neurons. We will compare neuronal populations activated by appetitive substances to those activated by aversive (bitter, sour) ones and how these neuronal populations correlate with specific feeding&#8208;related neuropeptide and transmitter systems of the brainstem taste relay nuclei. In addition, we will study whether taste quality representation in the brainstem is altered in mice with induced dysfunction (genetic knockout) in the detection of particular tastes. Finally, we will test whether neuronal activation in the primary taste nucleus is related to specific connectivity with taste axons contacting taste cells tuned to detect sweet and umami qualities.